The vertebrate fauna of the Upper Permian of Niger — II, Preliminary description of a new pareiasaur Christian A. Sidor1*, David C. Blackburn2 & Boubé Gado3 1Department of Anatomy, New York College of Osteopathic Medicine, Old Westbury, NY 11568, U.S.A. and Bernard Price Institute for Palaeontological Research, School of Geosciences, University of the Witwatersrand, WITS, Johannesburg, 2050 South Africa 2Department of Herpetology, Museum of Comparative Zoology, 26 Oxford St, Harvard University, Cambridge, MA 02138, U.S.A. 3Institut de Recherches en Sciences Humaines, Université Abdou Moumouni de Niamey, Niamey, Niger Received 4 June 2003. Accepted 7 November 2003 The skull of a new pareiasaur, Bunostegos akokanensis gen. et sp. nov., is described on the basis of a partial skull from the Upper Permian Moradi Formation of north-central Niger. Autapomorphies of the genus include the presence of three hemispherical bosses at the tip of the snout, an enlarged laterally projecting supraorbital boss positioned on each postfrontal, and additional, smaller bosses on the squamosal and supratemporal bones. Bunostegos is further characterized by a tab-like process of the nasal that articulates with the frontal, a pineal foramen located equidistant between the parietal-frontal and parietal-postparietal sutural contacts, a postparietal that is excluded from the caudal margin of the dorsal skull roof, and a blunt interpterygoid vacuity. The discovery of Bunostegos suggests an unsuspected degree of biogeographic endemism for central West Africa during the Late Permian. Keywords: Permian, Moradi Formation, West Africa, Niger, Pareiasauria, Parareptilia. INTRODUCTION (1972: pl. 1), but it was neither named nor described. The Beaufort Group of South Africa chronicles an impor- In November of 2000, a University of Chicago team led tant period of vertebrate evolution — the assembly of an by P.Sereno revisited the Moradi Formation. They discov- herbivore-based terrestrial ecosystem during the Middle ered a locality northwest of Agadez that produced the and Late Permian (Olson 1962; Bakker 1972; Reisz & Sues skulls of a new temnospondyl amphibian and the 2000). Although perhaps best known for its therapsid pareiasaur described in this contribution. (‘mammal-like reptile’) fauna (Hancox & Rubidge, 2001; Rubidge & Sidor, 2001), the Beaufort Group also enjoys MATERIAL the greatest diversity of pareiasaur taxa in the world. The specimen was collected from an intraformational Rubidge (1995) conservatively listed four pareiasaur conglomeratic unit of the Moradi Formation. The skull genera from South Africa, whereas Lee’s (1997b) more was preserved palate-up and had been eroded down to recent taxonomic revision recognized at least eight genera the level of the orbit. As a consequence, the lower jaw is comprising ten species. Importantly, the results of Lee’s absent and much of the palate is preserved only as impres- (1997b) study imply the sympatric co-occurrence of sion. The specimen was prepared at the Smithsonian pareiasaur herbivores: three genera co-occur within the Institution’s National Museum of Natural History in Tapinocephalus Assemblage Zone (AZ), four within the Washington, D.C. Cistecephalus AZ, and two within the Dicynodon AZ. Elsewhere in the world, pareiasaur remains are less SYSTEMATIC PALAEONTOLOGY abundant: three taxa are known from China, two taxa from Russia, and one each from Brazil, Germany, Pareiasauria Seeley, 1888 Morocco, Scotland and Zambia (Lee 1997b; Lee et al. 1997; Jalil 2001). Here we provide a preliminary description of Bunostegos akokanensis gen. et sp. nov. an unusual new pareiasaur from the Republic of Niger Etymology. Buno, knobby (Greek); stegos, roof (Greek), that suggests a distinct biogeographic province for West referring to its identification as a pareiasaur and the Africa near the close of the Palaeozoic Era (Sidor et al. knobby bosses that adorn the skull roof; Akokan, a town 2003). close to the type locality; -ensis (Latin), place or locality. The history of fossil discovery in the Moradi Formation Diagnosis. Medium-sized pareiasaur with three hemi- of Niger was reviewed by de Ricqlès & Taquet (1982). spherical bosses located at the anterior end of the snout; Although they discussed the collection of abundant nasal with a posterolateral tab-like process articulating vertebrate remains on expeditions in 1966, 1967 and 1969, with the frontal; elongate, laterally projecting postfrontal the only taxon to be formally named and described to date bosses overhanging orbits; hemispherical supratemporal is the large captorhinomorph Moradisaurus grandis boss located at posterolateral corner of skull roof; post- (Taquet 1969; de Ricqlès & Taquet, 1982). A pareiasaur frontal and supratemporal bosses with neck separating skull from the Moradi Formation was figured by Taquet globular head from skull roof; pineal foramen equidistant *Author for correspondence. E-mail: [email protected] from frontoparietal and parietal-postparietal sutures. ISSN 0078-8554 Palaeont. afr. (December 2003) 39: 45–52 45 Holotype. MNN-MOR72, a nearly complete cranium that has been eroded ventrally. Type Locality. Coordinates 18°47’01”N, 7°11’49”E, west of Arlit, Agadez Prefecture, Republic of Niger (Fig. 1). The locality lies in a conglomeratic layer of the Moradi Forma- tion, which is believed to be uppermost Permian, based on biostratigraphic data (Taquet 1972). DESCRIPTION Preservation MNN-MOR72 consists of a partial skull and several ‘skins’ of bone that preserve the external surface of the dorsal skull roof and temporal regions. Erosion has separated these ‘skins’from the remainder of the skull by a gap of between 0–2 cm, leaving only an endocast of the skull in certain places. The conglomeratic nature of the surrounding matrix, coupled with the specimen’s relatively spongy, pachyostotic bone, has made preparation and interpretation extremely difficult. In particular, this mode of preservation has limited our recognition of sutures between skull elements. Some sutures are visible on the internal surface of the ‘skins’ of bone, whereas others are visible on what remains of the skull itself. Rarely is a suture visible on the true external surface of the skull, which precludes a direct comparison with the pattern of other pareiasaurs. Figure 1. Geography and generalized Permian stratigraphy of the The palate and ventral surface of MNN-MOR72 is Republic of Niger. The position of Permian rocks is highlighted within extremely damaged, being planed-off by erosion. Some the outline of Niger. Abbreviations: Fm. = Formation, Izego. = bone and several sutures are evident in ventral view, Izegouandane, L = Lower, U = Upper. Stratigraphic subdivisions based although the majority of the palate is preserved only as on Ministère des Mines et de l’Hydraulique, Direction des Mines et de la Géologie (1977). impression. Substantial adhering matrix surrounds the occipital region and obscures this region’s structure. Only the dorsal process of the premaxilla is preserved. Further preparation of the occiput is risky due to the thin Ventrally this element is so badly eroded that the tooth- skull roof bones in this region. bearing ramus of the premaxilla is completely absent. The Figures 2, 3, and 4 show MNN-MOR72 with several of nasal descends along the posterior margin of the the ‘skins’of bone in place. Because the external surface of premaxilla’s dorsal process and may exclude the these ‘skins’ is backed by an approximately even amount premaxilla from participating in the preserved anterior of matrix, we believe that the overall shape of Bunostegos margin of the external naris. A similar condition was illus- is well portrayed. In the figures we have attempted to trated by Boonstra (1934: Pl. 2) for Dolichopareia angusta reconstruct the outline of the skull and project the place- (now Nochelesaurus angusta; Lee 1997b). In anterior view, ment of sutures onto its external surface. Caution should the pair of premaxillae form an inverted triangle that be used when comparing the sutural configuration of nearly reaches the base of a median boss. Bunostegos to that of other pareiasaurs because all of the The maxilla is typically a large, tooth-bearing element in sutures we illustrate are deep to some level (i.e., they are pareiasaurs that makes up much of the lateral surface of not on the true external surface of the bone). the snout. In addition, it forms much of the posterior margin of the external naris. In Bunostegos, the external Skull roof naris is incomplete and it is difficult to determine how Although its overall appearance is peculiar, Bunostegos is much, if any, of the maxilla remains. This uncertainty is a pareiasaur based on its possession of the following complicated by the poor delineation of the nasal and diagnostic characters: anapsid cranium, single fused lachrymal bones. postparietal located on the skull roof, medially directed Three hemispherical bosses are positioned at the rostral posterior choanae, and prefrontal-postfrontal sutural end of the skull roof: one boss is median and two are contact (Lee 1997a). Figures 2–4 demonstrate the impor- parasagittal. The median boss projects the furthest anteri- tant features of the genus, including three supranasal orly and is slightly smaller than the other two swellings. In bosses, laterally elongated supraorbital bosses formed by Pareiasuchus nasicornis, Lee et al. (1997) describe paired the postfrontals, and additional bosses extending laterally bosses above the external nares as separate ossifications